U.S. patent number 5,113,108 [Application Number 07/432,809] was granted by the patent office on 1992-05-12 for hermetically sealed electrostrictive actuator.
This patent grant is currently assigned to NEC Corporation. Invention is credited to Takeshi Nishizawa, Tetsuo Shirasu, Hidekazu Takada, Eiji Takahashi, Osamu Yamashita.
United States Patent |
5,113,108 |
Yamashita , et al. |
May 12, 1992 |
Hermetically sealed electrostrictive actuator
Abstract
A hermetically sealed electrostrictive actuator comprises a
metal case and a metal cap for housing an electrostrictive element
therein. The metal cap is provided with a pair of glass sealing
terminals to be connected to a pair of lead wires of the
electrostrictive element. The metal case is provided a flexible
region so as to follow the expansion and constraction of the
electrostrictive element without breaking the hermetic envelope of
the metal case and the metal cap.
Inventors: |
Yamashita; Osamu (Tokyo,
JP), Takahashi; Eiji (Tokyo, JP),
Nishizawa; Takeshi (Tokyo, JP), Takada; Hidekazu
(Tokyo, JP), Shirasu; Tetsuo (Tokyo, JP) |
Assignee: |
NEC Corporation (Tokyo,
JP)
|
Family
ID: |
27527855 |
Appl.
No.: |
07/432,809 |
Filed: |
November 6, 1989 |
Foreign Application Priority Data
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|
|
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Nov 4, 1988 [JP] |
|
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63-279741 |
Nov 4, 1988 [JP] |
|
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63-279772 |
Nov 15, 1988 [JP] |
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63-149158[U]JPX |
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Current U.S.
Class: |
310/328; 310/340;
310/346 |
Current CPC
Class: |
H01L
41/053 (20130101); H01L 41/083 (20130101) |
Current International
Class: |
H01L
41/083 (20060101); H01L 41/00 (20060101); H01L
41/053 (20060101); H01L 041/08 () |
Field of
Search: |
;310/323,328,346,340 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
|
409790 |
|
Dec 1945 |
|
IT |
|
60-19968 |
|
Feb 1985 |
|
JP |
|
60-39879 |
|
Mar 1985 |
|
JP |
|
2087659 |
|
May 1982 |
|
GB |
|
2193386 |
|
Feb 1988 |
|
GB |
|
Primary Examiner: Budd; Mark O.
Attorney, Agent or Firm: Laff, Whitesel Conte &
Saret
Claims
We claim:
1. A hermetically sealed electrostrictive actuator comprising: a
metal case having an opening and a bottom, an electrostrictive
element housed in said metal case and having a pair of lead wires,
one end of said electrostrictive element being fixed to said bottom
of said metal case, and a metal cap member fixed to the other end
of said electrostrictive element, said metal cap member and said
metal case being welded to seal said opening of said metal case in
an airtight manner a pair of glass sealing terminals associated
with said metal cap member so that said pair of lead wires are led
out from a side wall portion of said metal cap member via said
glass sealing terminals, and said metal case having a flexible
region so as to follow the expansion and contraction of said
electrostrictive element.
2. A hermetically sealed electrostrictive actuator as claimed in
claim 1, wherein said flexible region is formed by corrugating a
part of said metal case.
3. A hermetically sealed electrostrictive actuator as claimed in
claim 1, wherein said metal case is divided into two portions such
that, one is tubular member of bellows and the other is concave
metal lid.
4. A hermetically sealed electrostrictive actuator as claimed in
claim 3, wherein metal lid is divided into two portions so as to
sandwich a steel ball therebetween.
5. A hermetically sealed electrostrictive actuator as claimed in
claim 1, wherein said flexible region is formed at bottom portion
so as to form a diaphragm.
6. A hermetically sealed electrostrictive actuator comprising: a
metal case having an opening and a bottom, said opening having a
flange, an electrostrictive element housed in said metal case, one
end of said electrostrictive element being fixed to said bottom of
said metal case, a first metal cap member fixed to the other end of
said electrostrictive element, said first metal cap member having a
flange which is welded in an airtight manner to said flange of said
metal case, a pair of glass sealing terminals on said first metal
cap, a second cap member covering said pair of glass sealing
terminals, a pair of lead wires electrically connected through said
pair of glass terminals to said electrostrictive element, said lead
wires piercing a side wall of said second cap member, and said
metal case having a plurality of corrugated portions which follow
the expansion and contraction of said electrostrictive element.
7. A hermetically sealed electrostrictive actuator as claimed in
claim 6, wherein said second cap member has a projection with a
tapered part at its center.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric actuator, and more
particularly to a hermetical sealing structure for an
electrostrictive element.
Recently, piezoelectric actuators have become extremely promising
mechanical driving elements as precision positioning devices for
optical or magnetic disk heads, various kinds of optical devices,
precision machine tools and the like. Since the mechanical
displacement due to the piezoelectric effect is essentially
extremely minute, a plurality of electrostrictive ceramic layers or
piezoelectric ceramic layers are stacked with internal electrodes
as disclosed in the U.S. Pat. No. 4,681,667 issued on a Jul. 21,
1987. The mechanical displacement may be further increased by using
a mechanical amplification mechanism as is disclosed in the U.S.
Pat. No. 4,570,095 issued on Feb. 11, 1986.
In a conventional electrostrictive element using silver based
internal electrodes, migration easily takes place at exposed ends
of the internal electrodes in a humid atmosphere, and thus causing
a poor insulation characteristics. When a humidity test is given,
there occur numerous cases of discharge generation from the side
surface or the corner parts, creating a substantial obstacle to the
yield and the reliability of the products.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an
actuator with excellent moisture resistance.
According to the present invention, a hermetically sealed
electrostrictive actuator comprises a flexible metal envelope
containing an electrostrictive element therein. The metal envelope
consists of a metal case and a metal cap air-tightly sealed to each
other. The metal cap is provided with a pair of glass sealing
terminals connected to a pair of lead wires of the electrostrictive
element. The metal case is provided with a flexible region such as
bellows and corrugated portion so as to follow the expansion and
contraction of the electrostrictive element without breaking the
air-tightness of the metal envelope.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical sectional view showing a first embodiment of
the present invention.
FIG. 2 is a vertical sectional view showing a second embodiment of
the present invention.
FIG. 3 is a perspective view showing a third embodiment of the
present invention.
FIG. 4 is a vertical sectional view of the third embodiment shown
in FIG. 3.
FIG. 5 is a perspective view showing a fourth embodiment of the
present invention.
FIG. 6 is a vertical sectional view of the fourth embodiment shown
in FIG. 5.
FIG. 7 is a perspective view showing a fifth embodiment of the
present invention
FIG. 8 is a vertical view of the fifth embodiment shown in FIG.
7.
FIG. 9 is a vertical sectional view showing the details of the
laminated piezoelectric element shown in FIG. 8.
FIG. 10 is a vertical sectional view showing a sixth embodiment of
the present invention.
FIG. 11 is a perspective view of another structure of the
electrostrictive element.
FIG. 12 is a vertical sectional view of the electrostrictive
element shown in FIG. 11.
FIG. 13 is a characteristic curve showing the result of a humidity
test.
FIG. 14 is a vertical sectional view showing a seventh embodiment
of the present invention.
FIG. 15 is a vertical sectional view showing an eighth embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a circular stainless steel metallic member 7
with U-shaped sectional area equipped with a pair of lead terminals
81 is fixed to one end of an electrostrictive element 3. The lead
terminals 8 penetrate through each of a glass sealing terminal 8
connected with a lead wire 6 to an external electrode conductor of
the electrostrictive element 3. A circular strainless steel
metallic member 71 with U-shaped sectional area is fixed to the
other end of the electrostrictive element 3. Both ends of a
stainless steel cylindrical bellows 9 with inner diameter greater
than the other diameter of the electrostrictive element 3 and equal
to the inner diameter of the metallic members 7 and 71 are fixed to
the metallic members 7 and 71 so as to hermetically seal the
electrostrictive element 3.
Next, the method of manufacture of the electrostrictive actuator of
the present invention will be described.
First, a laminated body is prepared by forming a green sheet with
thickness of about 100 .mu.m by mixing an organic binder to
multicomponent solid solution ceramic powder having perouskite
crystal structure, coating it with a pastelike silver internal
electrode conductor layer, and after drying, laminating it into
tens of layers (64 layers, for example) and sintering. Since the
end portions of the silver internal electrode conductor layers are
exposed to the side surface of the laminated body, external
electrode conductors are formed after selectively covering the end
portions with an insulating glass film, and two comb-line
electrodes are formed by alternately connecting every other layer
of the silver internal electrode conductor layers. Then, lead wires
are connected to the external electrode conductors by soldering,
and the side surface alone is coated with a resin. The metallic
members 7 and 71 and the bellows 9 are attached to the
electrostrictive element 3, and the system is given a hermetic
sealing treatment. Namely, the electrostrictive element 3 is fixed
stand erect with an adhesive layer 11 to the inside bottom surface
of the metallic member 7 with two lead terminals 8 attached
thereto. Next, the lead wire 6 of the electrostrictive element 3
and the inner end of the lead terminal 81 attached to the metallic
member 7 are connected by soldering. Then, the bellows 9 is
attached from above so as to enclose the electrostrictive element
3, and the other metallic member 71 is fixed with adhesive layer 11
to the top end part of the electrostrictive element 3 so as to
cover the element. It is to be noted here that the spring constant
of the bellows 9 in the direction of expansion and contraction is
preferable to be less than one tenth of the generated force of the
electrostrictive element. Then, the hermetic sealing is completed
by welding both ends of the bellows 9 to the respective metallic
members 71 and along the entire circumference of each member by
electric arc welding.
FIG. 2 is a vertical sectional view of a second embodiment of the
electrostrictive actuator of the present invention. In this
embodiment, the bellows 9 and the upper metallic member 71 is
replaced by a bottomed bellows 91 with its one end (top part in the
drawing) blocked. The bottom of the bellows 91 is bonded to the top
face of the electrostrictive element 3 with the adhesive layer
11.
The present embodiment has an advantage in that the first
embodiment because of the deletion of the upper metallic member
71.
It should be noted that although the case of employing electric arc
welding as the method for hermetically sealing the bellows 9 and 91
with the metallic members 7 and 71, respectively, in the first and
the second embodiments, similar effect can also be obtained by
adopting other methods such as brazing, glass sealing and adhesion
with resin.
As described in the above, the present invention has an effect of
positively preventing the infiltration of moisture from ambient air
and enhancing the reliability of the device markedly by enclosing
an electrostrictive element within a hermetically sealed container
consisting of a bellows and metallic members.
Next, referring to FIG. 3 and FIG. 4, a third embodiment of the
present embodiment will be described. The electrostrictive element
3 is held in a hermetically sealed condition by the use of a
metallic case 92 and an airtight terminal 82 provided on one end
face of the electrostrictive element 3. A caplike metallic member
72 is placed covering the airtight terminal 82, and lead wires 61
are taken outside piercing through the metallic member 72 after
they are pierced through the airtight terminals 82 substantially
parallel to an electrostrictive effect generating axis 31.
Next, the assembly of the actuator will be described.
The metallic case 92 is fixed with the adhesive layer 11 to the
bottom surface of the electrostrictive element 3. The airtight
terminal 82 consists of a metal portion 820 and insulative portion
822. The metal portion 820 is fixed to the top surface of the
element 3 with the adhesive layer 11. A flange 821 of the metal
portion 820 and a flange 921 of the metallic case 92 are sealed to
each other by welding. The lead wires 61 are coated with insulative
material such as teflon. The take-out ports of the lead wires 61 of
the insulative portion 822 are sealed with a soldering material 825
after removing the insulative material of the lead wires 61. Then,
the caplike metallic member 72 which bends the lead wires 61, that
are taken out in parallel to the electrostrictive effect generating
axis 31 via the airtight terminal 82, orthogonally to the axis 31
is fixed with an adhesive or by soldering.
Referring to FIG. 5 and FIG. 6, a fourth embodiment of the actuator
of the present invention will be described. In this embodiment, a
metallic member 73 is used. The metallic member 73 has a base
surface that is not flat but is provided with a simply structured
projection having a tapered part at its center. With the provision
of such a projection there is obtained an advantage that the
positioning of the actuator element can be facilitated.
As described in the above, in the third and the fourth embodiments,
the lead wires that are taken out from either one of the end parts
of the element in parallel to the electrostrictive effect
generating axis are bent perpendicularly to the electrostrictive
effect generating axis, and a caplike metallic member 73 is fixed
to the actuator as a means for external mounting. By so arranging,
the following effects can be realized.
(1) In mounting the actuator to a certain product, the surface form
for mounting the actuator can be simplified.
(2) It becomes possible to transmit a stress generated in the
actuator by means of the totality of the stress generating
surface.
Next, referring to FIG. 7 to FIG. 9, a fifth embodiment of the
present invention will be described.
This electrostrictive element 3 is located within a metallic case
93 which has a corrugated part 931 so as to be able to expand and
contract in the direction of the electrostrictive element 3. A
platelike metallic stem 74 is fixed to the other end of the
electrostrictive element 3 with the adhesive layer 11. The metallic
stem 74 is provided with external terminals 83 and 84 that are
electrically connected to the external electrode conductors of the
electrostrictive element 3 via lead wires 63 and 64 and
hermetically sealed by hermetically sealing parts 831 and 841. The
metallic stem 74 is welded with the metallic case 93 at a contact
portion 932.
Next, the method of manufacturing the electrostrictive actuator of
the present embodiment will be described.
First, a small amount of an organic binder is added to prebaked
powder of electrostrictive material having lead nickel niobate Pb
(Ni 1/3 Nb 2/3) or lead titanate PbTiO.sub.3, for example, as main
components, a slurry is prepared by dispersing the above mixture
into an organic solvent, and an electrostrictive ceramic member 1
with thickness of about 10 .mu.m is formed by slip casting filming
method or the like with the slurry. Next, an internal electrode
conductor 2 is formed by depositing a conductive paste having a
mixed powder of silver powder and palladium powder in the weight
ratio of 7:3 on one side of the electrostrictive ceramic member 1
to a thickness of about 10 .mu.m by screen printing or the like.
After forming a laminated body by laminating a plurality of layers
of internal electrode conductors, and sintering it at about
1100.degree. C. for two hours, and a prismatic laminated sintered
body as the electrostrictive element 3 is formed. The end faces of
the internal electrodes 2.sub.1 to 2.sub.n-1 are exposed to the
outside by cutting the side surface of the laminated sintered body.
Next, insulating layers 4.sub.n to 4.sub.n-1 are formed by
alternately applying glass powder and giving sintering process to
the end parts of the internal electrode conductors 2.sub.1 to
2.sub.n-1 on a pair of opposed side faces of the laminated sintered
body by electrophoretic method. Subsequently, a pair of external
electrode conductors 51 and 52 are formed by applying a conductive
paste that contains silver powder as the principal component, in
order to connect every other one of the internal electrode
conductors 2.sub.1 to 2.sub.n-1, and by sintering the product.
Further, lead wires electrically connected to the external
electrode conductors 51 and 52 are installed. Next, a metal such as
stainless steel, phosphor bronze, german silver, monel metal,
beryllium copper, brass, nickel, inconel, 17-7PH, nickel sprun C
and aluminum is cold rolled into a cylinder closed on one end.
Then, a corrugated part 931 is formed in a part of the cylinder by
hydraulic push-in method or the like. The laminated sintered body
is then surrounded by the flexible metallic case 93 and a disklike
metallic stem 74 made of the same material as that of the metallic
case 93 and having a pair of hermetically sealed external terminals
83 and 84 made of an iron alloy, cobalt alloy, nickel or the like.
Then, the top and bottom faces of the electrostrictive element 3
are fixed to the bottom part of the metallic case 93 and to one
side of the metallic stem 74 via an adhesive 11 such as epoxy
resin. Finally, the manufacture is completed by sealing the contact
part 932 of the metallic stem 74 and the metallic case 93 by laser
beam welding method, electrobeam welding method, resistance welding
method, Tig welding method or the like in the vacuum, dry air, or
inert gas.
FIG. 10 is a vertical sectional view of a sixth embodiment of the
hearmitically sealed electrostrictive actuator of the present
invention.
The present embodiment can be obtained by providing a hole 751 that
communicates the interior of the metallic case 93 with the outside
in the metallic stem 75 in the fifth embodiment, and a rivet 12
that blocks the hole 751.
Next, the method for manufacture the present embodiment will be
described.
Up to the step of sealing, by welding, of the contact part 932 of
the metallic stem 75 and the metallic case 93 by means of laser
beam welding method, electrobeam welding method or the like, it is
the same as in the fifth embodiment. Next, moisture and the gaseous
components that remain within the metallic case 93 are expelled
through the hole part 751 provided in the metallic stem 75 by
heating the system in the vacuum environment at 150.degree. C. for
about one hour. Finally, after injecting an inert gas such as dry
air, N.sub.2, Ar or the like to substantially atmospheric pressure,
a metallic rivet 12 made of a copper alloy, aluminum or the like is
driven in or screwed in, and the system is completely sealed by
soldering it from above.
Referring to FIG. 11 and FIG. 12, shown structure is generally
called stack type, and internal electrode conductors 20 are formed
on both sides of the electrostricture ceramic members 10 sintered
beforehand in dislike form by leaving a pair of marginal parts 20a
and 20b so as to be symmetric with respect to the front and the
rear faces. Then, as shown in FIG. 12, the marginal portions 20a
and 20b where no internal electrode conductors are not exposed are
alternately aligned respectively on both ends of the side surface,
electrostrictive ceramic members 10.sub.l to 10.sub.n are connected
with an adhesive or the like, and a pillarlike laminated body 30 is
formed. Then, a pair of external electrode conductors 53 and 54
having a width smaller than that of the marginal portions 20a and
20b, whereby they are electrically connected alternately and
respectively to the exposed portions of the internal electrode
conductors 20.sub.1 to 20.sub.n. Finally, a stack type laminated
electrostrictive element is obtained by installing lead wires 65
and 66 that are electrically connected to the external electrode
conductors 53 and 54. Then, the manufacture is completed by
hermetically sealing the element obtained with a metallic case and
a metallic stem as in the fifth and the sixth embodiments.
In the electrostrictive elements shown in FIG. 7 to FIG. 12, when a
voltage is applied to the external terminals 83 and 84 from a
voltage supply part (not shown), the voltage is applied to both
ends of each of the electrostrictive ceramic members 1.sub.2 to
1.sub.n-1 via the lead wires 63 and 64, external electrode
conductors 51 and 52 and internal electrode conductors 2.sub.1 to
2.sub.n-1. Therefore, when the metallic stem 7 side is fixed, there
are generated a stress and a strain in the direction of the arrow
(FIG. 7).
FIG. 13 shows the result of evaluation of moisture resistance of
the actuator by the application of a DC voltage. When 1000 samples
of the fifth embodiment of the present invention are tested in an
atmosphere at 65.degree. C. with relative humidity of 90 to 95 % by
applying a rated voltage, there observed no defective product,
indicating a remarkable effect of the present invention.
As described in the above, the present invention has an effect of
completely blocking the infiltration of the moisture, chemicals,
oil, other gases and the like into the interior of the element by
improving airtightness markedly by hermetically sealing the
piezoelectric element with a flexible metallic case and a metallic
stem. Further, there is obtained an effect that a highly reliable
electrostrictive actuator which can absolutely reject the influence
of the moisture, chemicals, oil, other gases and the like by
markedly increasing the electric resistance of the surface of the
element by hermetically sealing the sealing port of the metallic
stem after replacing the gas inside the actuator.
Next, referring to FIG. 14, a seventh embodiment of the present
invention will be described. The electrostrictive element 3 is
formed by alternately laminating a piezoelectric ceramic member and
an internal electrode conductor layer, and providing a pair of lead
wires 6. One end of the electrostrictive element 3 is fixed to the
bottom surface of a metallic cap 76. The side surface of the cap 76
is provided with a pair of glass sealing terminals 8. Each glass
sealing terminal has a lead terminal connected to a respective lead
wire 6 of the electrostrictive element 3. Further at the opening
part of the metallic cap 76 there is welded along its entire
circumference a stainless steel bellows 94 having inner diameter
equal to the outer diameter of the metallic cap 76 and extending
beyond the other end of the electrostrictive element 3. On the
other end of the electrocstictive element 3, a metallic member 78
having a conical recess 782 at the center of one of the surfaces
and a recess 781 with substantially equal inner diameter as the
outer diameter of the electrostrictive element 3 on the other
surface, is placed covering the end of element 3 with the recess
781. Further, a metallic member 77 with substantially equal size as
the other diameter of the metallic cap 76 and having a conical
recess 771 on one surface, faces the metallic member 78 via a steel
ball 701 that is held between the recesses 782 and 771, and is
welded along the entire circumference to the bellows 94 on the
opening side of the bellows 94.
Next, the assembly of the electrostrictive element of the present
invention will be described.
First, the lead wires 6 of the electrostrictive element 3 are
connected by soldering to the respective lead terminals 81 of the
metallic cap 76. Then, the electrostrictive element 3 is placed in
the bellows 94 which is welded to the metallic cap 76, and the
element 3 is fixed to the inner bottom surface of the metallic cap
76 with an adhesive so as to stand erect there. Next, the recess
781 of the metallic member 78 is fixed to the upper end part of the
electrostrictive element 3, and the metallic member 77 is fixed to
the opening part of the bellows 94 so as to hold the steel ball 701
between the conical recess 782 of the metallic member 78 and the
conical recess 771 of the metallic member 77. Finally, the assembly
is completed by welding the metallic member 77 and the bellows 94
along their entire circumferences. When the electrostrictive
element 3 thus completed is attached between the mounting members
121 and 122 of the actuator, and a voltage is applied between the
lead terminals 8, there is generated a desired displacement in the
direction to separate the mounting members 121 and 122 by
expansion.
As described in the above, the present embodiment is given a
construction in which two metallic members are provided at one end
of the electrostrictive element so as to hold a steel ball freely
rollably between the opposing faces of the metallic members.
Therefore, it becomes possible to establish a close contact between
the respective end surfaces of the electrostrictive element and the
mounting surfaces of the mounting members, without requiring a high
accuracy finishing of both end surfaces of the electrostrictive
element, both end surfaces of the upper and lower metallic members,
and both end surfaces of the mounting members, and a high accuracy
parallelism between both end surfaces of the mounting members.
Since a desired displacement can be obtained with the above
construction, the present embodiment has an effect to reduce the
manufacturing cost markedly.
FIG. 15 is a vertical sectional view of an eighth embodiment of the
electrostrictive actuator of the present invention.
The electrostrictive element 3 is installed within a stainless
steel cylindrical metallic member 79. The metallic member 79 is
provided with a pair of glass sealing terminals 8. The other end of
the electrostrictive element 3 and the opening end of the metallic
member 79 are fixed with a stainless steel diaphragm 95 having
outer diameter equal to the outer diameter of the metallic member
79.
Next, the assembly of the present embodiment will be described.
The electrostrictive element 3 manufactured according to a method
similar to the conventional method is fixed with an adhesive to the
inner bottom surface of the metallic member 79 so as to stand erect
there. Next, the lead wires 6 of the electrostrictive element 3 and
the inner ends of the lead terminals 81 attached to the metallic
member 79 are respectively connected by soldering. Then, the
diaphragm 95 is fixed to the top surface of the electrostrictive
element 3 with an adhesive. Here, the spring constant of the
diaphragm 95 in the direction of expansion and contraction is
preferable to be one tenth of the generating force of the
electrostrictive element 3. Finally, hermetic sealing is completed
by welding the circumferential end of the diaphragm 95 to the
entire circumference of the metallic member 79 by electric arc
welding.
It is to be noted that the shape of the diaphragm 95 shown in the
present embodiment has one crest, but needless to say it may have a
plurality of crests or have an indefinitely shaped waveform.
As described in the above, the eigth embodiment has an effect of
making it possible to manufacture products with high reliability
that can withstand mechanical vibrations or shocks by enclosing the
electrostrictive element in a container consisting of a diaphragm
and a metallic member.
* * * * *